1. Field of the Invention
The invention relates to a configurable logic circuit arrangement comprising at least one multiplexer for switching logic signals, said multiplexer comprising one or more data inputs and one or more control signal inputs.
2. Description of the Related Art
A multiplexer enables the selection of one of n data lines by means of log to the base 2 of (n)+1 control lines. This is connected to the output of the MUX and it forwards the logic signals in this way. Programmable logic devices (PLD) acquire their flexibility through the configurability of the data processing (logic block) and the wiring (paths). In a typical PLD, the area proportion of the paths is approximately 75% and that of the logic elements is about 25%.
Path multiplexers (or router mux), that is to say multiplexers in which active signal paths with propagation-time-variant signal values are connected, are widespread in programmable logic devices. Multiplexers which are also referred to as data selectors serve for changing over from one of a plurality of inputs to an output. Multiplexer structures of this type are used in programmable logic devices for routing the signals. Here a data input is selected before operation of the circuit, which data input carries signal values that change during operation, while the selection of the data input, that is to say of the signal value source, remains constant.
Multiplexers are thus the crucial components in the case of the configurable wiring. In the simplest case, a binary-value input of a multiplexer controls the assignment of at least two data inputs to an output.
It is known to configure paths having multiplexers in a configuration or programming operation by means of configuration signals. This operation has to take place before operation of the circuit. With this type of multiplexer, also referred to as router mux, a nonvolatile configuration of the control inputs is performed, for example by means of a mask, a fuse, a flash cell or a transistor configured in nonvolatile fashion, so that during normal operation, that is to say during the propagation time of the data signals, the multiplexer cannot be changed. Devices also exist whose configuration is based on the storage of the items of information in volatile SRAM cells. Operating means for propagation time configuration are not provided, however. Although structures of this type have proved worthwhile overall, it is regarded as a disadvantage that very many lines are needed for the configuration of the control inputs and a configurable multiplexer correspondingly requires a considerable peripheral area. The case may even arise wherein the circuit outlay for the configuration is higher than the outlay for the logic processing in the logic block. A further disadvantage can be seen in the fact that the lines required for the configuration and their logic devices are subsequently, that is to say after the configuration, no longer available for some other utilization in the course of operation (normal operation).
A very large portion of the configuration lines and of the associated logic elements possibly remain unutilized in conventional logic circuit arrangements.
The following multiplexer structures occur in logic blocks: logic mux, switch mux, LUT mux. Parameters that distinguish these MUX are: configuration operation; number of memory cells; what remains configurable. It follows from this that either the storage of the data and configurations are absent or, in the course of operation, a reconfiguration or change of the signals is not possible and the assigned periphery cannot be utilized any further.